Date of Completion

8-26-2014

Embargo Period

8-25-2014

Major Advisor

Dr. Steven Suib

Associate Advisor

Dr. Christian Bruckner

Associate Advisor

Dr. Nicholas Leadbeater

Associate Advisor

Dr. Edward Neth

Associate Advisor

Dr. Mark Peczuh

Field of Study

Chemistry

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Pre-ceramic polymers are attractive, low cost materials for the manufacture of ceramic fibers and matrix materials in Ceramic Matrix Composites (CMCs). A new pre-ceramic polymer, an ethanol-modified polyvinylsilazane (PVSZ), was synthesized and characterized. The PVSZ polymer has been previously shown to be a viable precursor for silicon nitride and silicon carbide based ceramics, but lacked stability when exposed to air. The PVSZ polymer was synthesized via the ammonolysis of trichlorovinylsilazane in tetrahydrofuran (THF), and then reacted with ethanol to form the ethanol-modified PVSZ. The PVSZ polymer and ethanol-modified PVSZ resin were each characterized with Attenuated Total Reflectance spectroscopy (ATR), 1H Nuclear Magnetic Resonance (1H-NMR), and Gel Permeation Chromatography (GPC), Thermogravimetric Analysis (TGA), Residual Gas Analysis (RGA), and X-Ray Powder Diffraction (XRD) of the ceramic char after pyrolysis in various atmospheres.

A second new modified PVSZ was also synthesized. Rather than use ethanol, a second silane monomer was added during synthesis, with the intent of stabilizing the polymer without incorporating oxygen. The new end cap modified PVSZ (EC-PVSZ) was characterized using the same methods outlined for the ethanol-modified PVSZ. Both modified systems demonstrated improved shelf-life.

Chemical Vapor Deposition (CVD) was employed to deposit ZnO/SiO2 interfacial coatings onto Nextel-440™ fabric. A new low pressure CVD (LP-CVD) furnace was designed to deposit SiO2 under reduced pressure. The effects of temperature, precursor amounts, and coating thicknesses were examined to optimize the mechanical strength of the coated fabric.

Tensile testing of the fibers was used to evaluate the impact of the coating processes on the fabric’s strength. Coated fabric was evaluated by X-Ray Diffraction, Scanning Auger Microscopy (SAM), and Scanning Electron Microscopy (SEM).

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